Astronomers in Switzerland find new 3-planet solar system

Published 4:00 am, Thursday, May 18, 2006

Astronomers hunting for solar systems beyond our own have discovered a remarkable new one in which three planets, roughly the size of Neptune, are circling a nearby sunlike star, which is surrounded apparently by a dense belt of asteroids.

The inner two planets appear to be made mainly of rock -- like Earth -- while the third may have an envelope of gas around a core of rock and ice, the astronomers say.

None is likely to harbor life, although the outermost planet lies within what astronomers call the "habitable zone." The habitable zone in our solar system is where conditions of temperature and light have made life possible on Earth.

The discovery, exploiting an extremely precise new measuring system, suggests that many more relatively small planets should soon be detectable around other stars in the Milky Way galaxy, astronomers say.

A report on the newfound planetary system is being published today in the journal Nature by a team at the Geneva Observatory in Switzerland, headed by veteran planet hunters Christophe Lovis and Michel Mayor. They discovered the planets with a powerful new instrument called the High Accuracy Radial velocity Planet Searcher, or HARPS for short, at the European Southern Observatory high in Chile's Atacama desert.

The star at the center of the three circling planets lies within the constellation Puppis, the poop deck, which earlier astronomers had identified as part of a larger constellation called Argo Navis, the ship of the Argonauts in ancient Greek mythology. The star itself is catalogued as HD69830, and lies about 40 light-years from Earth. It is barely visible to the naked eye and can only be observed from below the equator.

The asteroid belt that appears to circle the star somewhere among the planets had been detected earlier by NASA's Spitzer space telescope now flying in orbit around Earth.

The discovery by the Geneva team is "quite beautiful," said Geoffrey Marcy, the UC Berkeley astronomer who with his colleagues has long been on a hunt for more exoplanets -- distant planets in solar systems outside of ours.

More than 180 of those solar systems have been discovered since the quest began more than a decade ago, and Marcy's group and the Swiss team have found more than 95 percent of them, Marcy said.

"This new system," he said, "is gorgeous and unique. It appears to have three 'Super-Earths.'

"Certainly their existence, especially in a system, suggests that Earthlike planets are common in the universe. Our Earth may well be a typical rocky planet, albeit one located at just the right distance from the sun to allow water to be in liquid form, the prerequisite for life."

The outermost planet -- or third planet from the sun -- in the so-called habitable zone of this new system is at least 18 times more massive than Earth, Marcy noted, so life there, no matter what the temperature, would be highly improbable.

"Even single-cell life would sink to great depths, where there is enormous pressure similar to the pressure in the mantle of the Earth's interior, and crush any cells," he said.

Of the three planets, the innermost one is barely more than 7 million miles from its star, while the second planet's orbit carries it about 17 million miles out. The outermost planet flies around the star nearly 60 million miles out -- compared to Earth's average distance of 93 million miles from our sun.

"This is indeed a fascinating discovery," said Harvard astronomer David Charbonneau in an e-mail. Charboneau leads another team of exoplanet hunters, and in a commentary published in Nature today, he noted that "exquisite" measurements by the Geneva group's new search instrument "suggest that the search for habitable planets might be easier than assumed." Reflecting the fascination of all his colleagues, Charbonneau added, "The architecture of this particular planetary system bears some intriguing similarities to that of our own solar system."